echo: make -e and -E override each other

src/uu/echo/src/echo.rs

@@ -154,13 +154,15 @@ pub fn uu_app() -> Command {
             Arg::new(options::ENABLE_BACKSLASH_ESCAPE)
                 .short('e')
                 .help("enable interpretation of backslash escapes")
-                .action(ArgAction::SetTrue),
+                .action(ArgAction::SetTrue)
+                .overrides_with(options::DISABLE_BACKSLASH_ESCAPE),
         )
         .arg(
             Arg::new(options::DISABLE_BACKSLASH_ESCAPE)
                 .short('E')
                 .help("disable interpretation of backslash escapes (default)")
-                .action(ArgAction::SetTrue),
+                .action(ArgAction::SetTrue)
+                .overrides_with(options::ENABLE_BACKSLASH_ESCAPE),
         )
         .arg(Arg::new(options::STRING).action(ArgAction::Append))
 }

tests/by-util/test_echo.rs

@@ -117,6 +117,19 @@ fn test_escape_newline() {
         .stdout_only("\na\n");
 }
 
+#[test]
+fn test_escape_override() {
+    new_ucmd!()
+        .args(&["-e", "-E", "\\na"])
+        .succeeds()
+        .stdout_only("\\na\n");
+
+    new_ucmd!()
+        .args(&["-E", "-e", "\\na"])
+        .succeeds()
+        .stdout_only("\na\n");
+}
+
 #[test]
 fn test_escape_no_further_output() {
     new_ucmd!()